What Is a Spherical Plain Bearing?
A spherical plain bearing has a spherical contact between the inner and outer rings. Unlike rolling bearings, spherical plain bearings have no rolling elements, so they are plain bearings with surface contact. There are various types of spherical plain bearing, which can be broadly classified into oilless and non-lubricated types according to the type of sliding surface.
Because of the spherical contact, a spherical plain bearing is capable of self-aligning, and because of their structure, they can carry axial loads in both radial and axial directions simultaneously.
Uses of Spherical Plain Bearings
Because of their surface contact and the absence of rolling elements, spherical plain bearings can support large loads and are used mainly in situations where heavy loads are applied at low speeds. On the other hand, because of the surface contact, they are rarely used in high-speed rotating environments, even when heat generation is suppressed by lubrication, etc.
Because they are often used in the rod ends of cylinders, some manufacturers offer a lineup of bearings with rod ends or with rod ends and bearings in one piece.
Principle of Spherical Plain Bearings
Spherical plain bearings hold the shaft by bringing the inner and outer rings into contact with spherical plain bearings. The spherical surface sliding on the contact surface holds the shaft without causing friction, but care must be taken because uneven wear may occur due to lack of maintenance or depending on the conditions of use.
Spherical plain bearings can be classified into two types based on their structure: lubricated and non-lubricated. Oil-lubricated types do not have a groove to incorporate the inner ring, so there is no place to receive a concentrated load, and thus the load carrying capacity can be increased. In contrast, the oilless type does not run out of oil and thus has excellent high-speed rotation and wear resistance.
In addition, spherical plain bearings require dimensional tolerances to be specified for the inner and outer rings during assembly and for the shaft and housing during mounting. Therefore, if the load is applied non-uniformly due to the wrong selection of dimensional tolerances, it can cause bearing deformation and wear, resulting in vibration and shortening the life of the bearing.